1. Field of the Invention
This invention relates to a method of inspecting a floppy disk casing which is for rotatably accommodating therein a magnetic recording disk and is provided with liners on the inner surfaces of the upper and lower walls thereof for cleaning the sides of the recording disk, and more particularly to a method of inspecting such a floppy disk casing for porjection of a part of the liners beyond an edge of the casing.
2. Description of the Prior Art
As is well known, a floppy disk or a micro floppy disk used as a recording medium for a computer, an electronic still camera and the like generally comprises a casing and a magnetic recording disk accommodated for rotation in the casing. The casing is generally referred to as a "jacket" or "shell", and is generally provided with liners formed of fiber material and bonded to the inner surfaces of the upper and lower walls thereof.
The casing is provided with a magnetic head receiving opening for giving the magnetic head access to the magnetic recording disk in the casing, and the liner is bonded to the casing to the edge of the magnetic head receiving opening to circumscribe the opening. When the liner is bonded to the casing in a wrong position, or when the liner fluffs up, the liner is apt to project into the magnetic head receiving opening to cause drop-out or to prevent recording and reproduction.
Accordingly, the floppy disk casing must be inspected for such projection of the liner in the manufacturing step of the floppy disk. Conventionally, a light beam is projected from one side of the casing to pass near the edge of the opening and the reflected part of the light beam is detected by a photodetector such as a TV camera and a linear image sensor, and whether the liner projects beyond the edge of the opening is determined on the basis of the amount of light received by the photodetector.
However, when the color of the casing resembles the color of the liner (generally white) and the reflectances of the casing and the liner approximate each other, it is difficult to distinguish light reflected by the liner from that reflected by the casing, and accordingly, in order to make a precise inspection, the light beam must be precisely positioned with respect to the casing to impinge solely upon the projecting portion of the liner, if any, and not to impinge upon the casing.